Recently, various kinds of display devices which include a liquid crystal display device have been used for various purposes. In a general display device, a single pixel includes three sub pixels for displaying red, green and blue which are the three primary colors of light, and thus producing a color display is possible.
However, a conventional display device has a problem in that a displayable color range (called a “color reproduction range”) is narrow. FIG. 14 illustrates the color reproduction range of a conventional display device which performs display using three primary colors. FIG. 14 is an xy chromaticity diagram of an XYZ colorimetric system, and a triangle, which includes three points corresponding to three primary colors of red, green, and blue as apexes, indicates the color reproduction range. In addition, in the drawing, various object colors which are clarified using pointers and which exist in the nature (refer to NPL 1) are plotted using x marks. As understood from FIG. 14, the object colors which are not included in the color reproduction range exist, and it is difficult for a display device which performs display using three primary colors to display some of the object colors.
Here, in order to increase the color reproduction range of the display device, a method for increasing the number of primary colors, which are used for display, by four or more has been proposed (refer to PTL 1).
For example, like a liquid crystal display device 600 illustrated in FIG. 15, a single pixel P includes four sub pixels of a red-sub pixel R, a green-sub pixel G, a blue-sub pixel B and a yellow-sub pixel Ye, and thus it is possible to increase the color reproduction range. Otherwise, similar to a liquid crystal display device 700 illustrated in FIG. 16, a single pixel P may include five sub pixels of a red-sub pixel R, a green-sub pixel G, a blue-sub pixel B, a cyan-sub pixel C, and a yellow-sub pixel Ye, and, like a liquid crystal display device 800 illustrated in FIG. 17, a single pixel P may include six sub pixels of a red-sub pixel R, a green-sub pixel G, a blue-sub pixel B, a cyan-sub pixel C, a magenta-sub pixel M, and a yellow-sub pixel Ye. When four or more primary colors are used, it is possible to increase the color reproduction range, compared with the conventional liquid crystal display device which performs display using the three primary colors. In the specification, a display device which performs display using four or more primary colors is generally called a “multiple-primary color display device”, and a liquid crystal display device which performs display using four or more primary colors is generally called a “multiple-primary color liquid crystal display device”. In addition, a general display device according to the related art which performs display using the three primary colors is generally called a “three-primary color display device”, and a liquid crystal display device which performs display using the three primary colors is generally called a “three-primary color liquid crystal display device”.
An RGB format, a YCrCb format, or the like is a general format of a video signal which is input to the three-primary color display device. Since a video signal which has the format includes three parameters (in other words, a 3D signal), the brightness of the three primary colors (red, green, and blue) which are used for display is unambiguously determined.
In order to perform display using the multiple-primary color display device, it is necessary to convert the video signal which has a format for the three-primary color display device into a video signal which includes a larger number of parameters (four or more parameters). The video signal which corresponds to the four or more primary colors is called a “multiple-primary color video signal” in the specification.